Original photo by jijomathai/ Adobe Stock
Even though you experience life as a continuous, unchanging flow of time, most of the cells in your body are constantly being renewed. Through a process called cell turnover, old cells die and are replaced by new ones, meaning much of your biological makeup is far younger than your chronological age.
Aging still occurs because some cells don’t regenerate, renewal slows in certain tissues, and even new cells can experience wear and tear over time. Nonetheless, on average, the cells in an adult human body are estimated to be only 7 to 10 years old — so even in middle age, much of your body is biologically closer to that of a child than to that of an elderly adult.
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It's a factThe delicate sensory hair cells in the inner ear don’t regenerate once they’re damaged or lost — which is why hearing loss from aging or loud noise is often permanent.
Scientists have been able to estimate cellular ages thanks to carbon-14, a naturally occurring radioactive form of carbon that entered the atmosphere in large quantities during above-ground nuclear weapons testing in the mid-20th century. When cells divide, carbon-14 from the environment becomes permanently embedded in their DNA, effectively “dating” the moment each cell was born. By measuring the carbon-14 levels of different tissues, researchers can determine how often various parts of the body renew themselves.
The pace of renewal isn’t uniform across all tissues. For example, skin cells regenerate roughly every few weeks, the gut lining every few days, red blood cells about every four months, and liver cells approximately every year. Then there are cells — including most neurons in the brain’s cerebral cortex and the eyes’ inner lens cells — that can last an entire lifetime. Because some critical cells don’t regenerate and other new cells gradually accumulate damage, the body experiences functional decline and aging, even as most cells continue to turn over.
Numbers Don't Lie
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Long after pregnancy, a mother’s body can still contain cells from the fetus, a phenomenon known as ______.
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Long after pregnancy, a mother’s body can still contain cells from the fetus, a phenomenon known as microchimerism.
Your sense of taste depends on some of the fastest-renewing cells in your body.
Like other cells in your body, the specialized cells in taste buds — the taste receptor cells that detect sweet, bitter, salty, sour, and umami flavors — are continually replaced throughout your lifetime. Those cells live only about eight to 12 days before being shed and replaced by new cells produced from progenitor cells in the tongue epithelium, the thin layer of tissue covering the surface of the tongue.
That rapid turnover helps explain why illnesses, injuries, or aging can temporarily alter taste perception. Because each new taste cell must form connections with nerves to transmit flavor information, anything that affects cell production or differentiation — including infections, inflammation, or age‑related changes — can cause shifts in your experience of how foods taste.
Kristina is a coffee-fueled writer living happily ever after with her family in the suburbs of Richmond, Virginia.
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